This invention relates to a process of heat transformation to convert the low-temperature waste heat from cooling circuits of block-type thermal power station (BTPS) reciprocating-piston combustion engines into steam or other heating media having a temperature required for operation by adopting the principle of the high-temperature heat pump according to the preamble of claim 1, and devices for realizing the process according to claims 17 to 24.
According to the state of the art, it is known to equip block-type thermal power stations with gas turbine or reciprocating-piston combustion engine drives the waste heat of which is coupled out in heat exchangers and is used for heating purposes. As far as this waste heat is produced in the exhaust gas it may be utilized in a waste-heat boiler to generate heating media at a pressure and a temperature as are required for operation. The low-temperature circuits to cool the charging air, oil, and cylinders of reciprocating-piston industrial combustion engines are designed for an inflow temperature of the cooling water of 70 to 80xc2x0 C. in the normal case and 110 to 125xc2x0 C. in special designs and for its heat-up rate by 5 to 10xc2x0 C. This low-temperature proportion, which comes up to 35 to 50% of the waste heat depending on the fuel and the construction of the engine, constitutes the limiting factor for the use of engine-powered BTPS in technical process industrial plants in many cases because it cannot be utilized to a sufficient degree in the plant. Although reciprocating-piston engines have a better mechanical/electrical efficiency factor, a more favourable behaviour under part-load and, because of the lower air surplus, a lower loss in the chimney of the waste-heat boiler industrial power/heat coupling plants are predominantly equipped with gas turbines the whole usable waste heat produced at a high temperature in the exhaust gas may be universally employed to heat the in-plant processes. Since gas turbines will present a good price-performance ratio only when in larger units and are dependent on high, uniform heat release because of their bad behaviour under part-load using them in small-size or medium-size plants is mostly uneconomical so that their power/heat coupling potentials which are downright interesting both economically and ecologically still are not fully exploited in many cases. Engine-powered BTPS which are used, in spite of the problems shown, in a few industrial enterprises exhibiting a particular ecological engagement are predominantly connected in such a way that low-temperature waste heat is used, as far as possible, to heat buildings or, if absorption cold-water units are connected therebetween, also to cool and air condition buildings where heating water of 70/90 or 110/125xc2x0 C. can be managed with as a maximum. The technical and organizational expenditure for the direct use of the low-temperature waste heat as a second heating medium in partial regions of commercial establishments and industrial enterprises, however, is so considerable and synchronizing the production and consumption by the various thermal energy carriers is so difficult that the xe2x80x9cemergency coolingxe2x80x9d of the energine needs to be turned on and the utilization of the xe2x80x9clower-valuexe2x80x9d low-temperature waste heat has to be dispensed with relatively often in the superior interest of meeting the steam and current demand in spite of careful works management.
In view of the problems depicted, efforts are made on the side of some engine producers to step up the admissible cooling-water inflow temperatures to the range of from 110 to 125xc2x0 C., on one hand, but a great number of authors have reported on researches and attempts to raise the low-temperature waste heat to an in-plant utilizable temperature level by means of high-temperature heat pumps using mechanical vapour compression or heat transformers according to the principle of absorption technology, on the other. However, success has passed hitherto beyond some single applications only in a few fields the common denominator of which is a relatively low raise in temperature because simple no-oil compressors which are not too expensive are available for pressure differentials of max. 1 bar and the ratio between recuperated energy and the one required for driving (calorific value, efficiency factor) is attractive economically.
Such applications are found, for example, on the xe2x80x9cwort coppersxe2x80x9d in brewing houses where large volumes of water evaporate at an ambient pressure or pressure slightly above it, are compressed by about 0.5 bar by means of compressors which mostly are mechanical or occasionally are even steam-jet vapour compressors, and are re-used immediately and via the shortest way possible, in very largely dimensioned heat exchangers just to fire the wort copper from which they were evaporated a few instants before. A report was made about this as early as in 1981 by W. STRUCK in his article xe2x80x9cMxc3x6glichkeiten und Grenzen von Hochtemperatur-Wxc3xa4rmepumpenxe2x80x9d, published in volume VII of the series xe2x80x9cWxc3xa4rmepumpentechnologiexe2x80x9d of the Vulkan Verlag, Essen, rating the degree of primary energy utilization of the gas engine driven plant therein at the considerable factor 5.3. It is from the same source that the description of a BTPS may be taken, which uses recooling of the engine cooling water to 75xc2x0 C. by partial evaporation at a saturation pressure of 0.4 bar and vapour compression to 2.7 bar, which corresponds to a temperature of 130xc2x0 C. of the heating medium (which is steam in this case). Such plants which already come very close to the subject matter of the present application for a protective right, however, have not pushed their way in practice because the relationship between the mechanical energy to be employed to the recuperable thermal energy is not correct either ecologically or economically and the water/steam range of the plants which is open to the engine cooling circuit, and even at a negative pressure, on one hand, and to the heating circuits of the plant, on the other, poses serious sealing and maintenance problems.
From U.S. Pat. No. 4,803,958, a process to xe2x80x9cpumpxe2x80x9d the waste heat from the cooling circuit of a combustion engine into steam of a higher temperature by means of a high-temperature heat pump powered by the heat content of the combustion engine exhaust gases has become known wherein the working medium withdrawn from the cooling circuit (water) is evaporated directly. The heat pump is configured as an absorption heat pump in this application and causes the working medium vapours to be compressed by absorption in an absorber, pumping of the solution to the desorber pressure, and desorption in a desorber by means of the heat content of the exhaust gases of the combustion motor.
On the basis of the depicted state of the art, it is an object of the invention to provide a heat transformation process and devices for realizing the process according to the principle of the high-temperature heat pump by means of which the waste heat not only of the hot exhaust gas, but also the one of a proportion as large as possible of the low-temperature waste heat from the cooling circuits for cylinders, the lubricating oil, and the charging air/fuel mix may be used up to a lower temperature limit to be fixed for each project by conversion into the in-plant common heating medium in a technically reliable manner and at an economical relationship between the investment and operating expenditures to the output from the recuperated energy in reciprocating-piston engine BTPS for the heat supply to commercial and industrial enterprises.
Specifically, it is the processes and devices according to the teachings of claims 3, 5, 6, and 7 which meet the requirement of technical reliability by avoiding designs affected by high risks of operation, maintenance, and repair such as a negative pressure in the low-pressure area of the heat transformer or direct supply of the engine cooling water to the in-plant heating medium.
According to the invention, an economical relationship of the investment and operating expenditures to the yield and output of the heat transformer is aimed at by the fact that
according to the teachings of claims 3 and 7 to 13, the waste heat produced in the low-temperature range is treated and selected in such a way that its recuperation may be performed to the largest extent possible (heat volume) and in the best quality possible (temperature), which is aimed at achieving an optimum thermal efficiency factor without recurring to the mechanical/electrical efficiency factor or by recurring to it as little as possible,
according to the teaching of claim 12, the power demand for vapour compression is minimized by an extensive utilization of the low-temperature waste heat in the non-treated condition of its production, and
according to the teachings of claims 1 and 14 to 23, the energy for the heat transformation of the low-temperature waste heat is provided, to an available extent, from the higher-value engine waste and at least a recourse to high-quality mechanical and/or electrical energy fir vapour compression and the concomitant reduction of the BTPS mechanical/electrical efficiency factor are avoided.
Hence, the invention has the following substantial advantages:
1. Reciprocating-piston engine BTPS with their mechanical/electrical efficiency factor superior to that of the gas turbine BTPS and with their more favourable behaviour under part-load may also be used, while permanently and completely utilizing the waste heat for power/heat coupling, upon installation of the proposed heat transformer, also in those plants, which do not have a sufficient demand (i.e. no demand equivalent or time-synchronized to their power and steam consumption or, generally stating, their high-temperature heating medium consumption) for the low-temperature waste heat produced in the BTPS cooling circuits.
2. As a result of driving the heat transformer which is fully or partly effected by utilizing the energy of the engine exhaust gas according to the proposed processes and devices, the mechanical/electrical efficiency factor of a power/heat coupling plant is not diminished at all or is diminished far less than if electrically or mechanically driven high-temperature heat pumps are used according to known processes and devices.
3. The protection against the penetration of air and/or oil resulting from leakages in the low-temperature range from the engine cooling circuits to the vapour compressor of the thermal transformer, which is brought about by measures to avoid any negative pressure in the high-temperature heat pump and the in-plant heating system remedy the serious process and construction-related reliability lacks of the high-temperature heat pump BTPS which have been known hitherto according to the state of the art.
4. The technical advantages of the reciprocating-piston combustion engine BTPS including the proposed heat transformer make it economically useful to employ the ecologically worthwhile power/heat coupling in a multiplicity of preponderantly small-sized and medium-sized commercial establishments and industrial enterprises the heating power demand of which for gas turbine BTPS is too low and/or too non-uniform and which, apart from their steam demand for the low-temperature waste heat of common reciprocating-piston BTPS, have no sufficient and time-synchronized use therefor.
Aspects of the invention relate, amongst other things
1. a process of low-temperature heat recuperation which makes it possible to gain the waste heat from a proportion as large as possible of the BTPS engine cooling circuits at a temperature which is so far above the boiling-point of the heat transformer working medium that there is no drop below the ambient pressure in any point of vapour evaporation and compression. This ensures that leakages due to media exiting to the outside are signaled and suction of air or oil into the working medium are prevented and that a high suction pressure advantageous for the power demand for vapour compression and a low suction volume of the working-medium steam favourable for the construction expenditure of the compressor are achieved and an expensive sealing against a negative pressure are avoided;
2. a process of vapour compression and heating power provision in the high-pressure region of the heat transformer according to the criteria of para 1 such that the energy required for vapour compression from the saturation pressure of low-temperature heat recuperation to the saturation pressure of the in-plant heating medium is gained as far as possible from the heat content of the engine exhaust gas by converting it into superheated high-pressure motive steam and expanding it to the pressure of the in-plant heating medium while being deprived of compression work or by using it for driving a hot-air prime mover according to the Stirling principle.
Embodiments of the invention for realizing the process according to the invention are shown in the drawing and are described below.